A. Field of the Invention
The present invention relates generally to the field of manipulator apparatus and more particularly to an energy efficient control arrangement for manipulator apparatus.
B. Description of the Prior Art
Control arrangements for manipulator apparatus are disclosed for example in U.S. Pat. Nos. 4,362,978, 3,661,051, 4,086,522, 4,132,937, 4,140,953, 4,150,326, 4,163,183, Re. 31,208, and 4,105,937. Typical manipulator apparatus disclosed in these patents is arranged to control the movement of a manipulator arm in a plurality of axes to perform repetitive work cycles in a repeat mode in accordance with stored command signal data for defined program steps; the stored command signal data being acquired in a teach mode. Servo control loops and feedback techniques are utilized to control movement of the manipulator arm in response to the stored command signal data in either a point-to-point mode or a continuous path mode. Servo control valves are utilized in one or more of the axes to provide pressurized fluid from a source to either end of a cylinder to move a piston that is slidably mounted in the cylinder. The pressurized fluid is selectively provided to the cylinder by control of the servo valve. In the point-to-point mode, the servo valve is opened to provide acceleration of the piston until a maximum slew velocity is reached. The servo valve is then controlled to move the piston at the maximum slew velocity until the desired final position is approached whereupon the servo valve is controlled to decelerate the piston with various combinations of position, velocity and acceleration feedback being utilized in the overall control loop.
U.S. Pat. No. 3,744,032 discloses a control arrangement wherein a limp hand mode is established for moving workpiece applications. In the limp hand mode the hydraulic actuators are bypassed when the weld jaws on the manipulator arm engage a moving car body. This allows the car to pull the compliant manipulator arm along the moving path and reduces the number of required recorded points. When the bypass is open at the beginning of a weld to interconnect the ends of the actuator cylinder, the servo valve that normally controls movement of the actuator is disabled.
Other control arrangements provide adaptive control of apparatus wherein stored command data is updated and refined during successive cycles of operation to provide optimized command data. Adaptive systems of this type and other control apparatus are disclosed for example in U.S. Pat. Nos. 3,555,252, 3,917,930, 3,974,432, 3,551,656, 3,757,187, 3,770,947, 3,889,238, 3,825,731, 3,969,723, and 4,021,651.
While the aforementioned control systems are generally suitable for their intended use, it would be desirable to provide energy efficient control of manipulator apparatus wherein the pressurized source is only required for movement of the arm during the acceleration phase; the pressurized source not being connected for supplying the cylinder after the slew velocity is reached.